A simple and effective method for learning a foreign language is to read entertaining literature in that language. However, the need to constantly refer to a dictionary often makes what should be an enjoyable experience tedious, thus discouraging the reader.
One solution to this problem involves printing the foreign language text and its familiar language translation on opposing pages of a book so that quick reference may be had to the translation. This has been implemented in prayer books and the like but the relatively extensive eye movement required to refer to the translation interrupts the reading of the foreign language text sufficiently to destroy the flow of the reading process.
Alternatively, it has been proposed to print the familiar language translation and a foreign language text directly adjacent to one another, effectively interleafing lines of the foreign and the familiar text. U.S. Pat. No. 3,126,647 discloses this type of arrangement in which the familiar text is printed in such small size type as to be unreadable to the normal unaided eye. When the familiar language translation of a word in the foreign text is required, a hand magnifying glass is brought into position over the translation, rendering it visible. Similarly, U.S. Pat. No. 4,891,011 discloses a system in which a familiar language translation is printed directly beneath the foreign language text using a medium which is generally invisible to the human eye unless exposed to light of a specified frequency range, such as ultraviolet light. The reader is provided with a portable light source of the specified frequency which may be used to illuminate the translation when required.
These arrangements require that the lines of the foreign text be spaced relatively widely from one another, and require the reader to move the device which will reveal the foreign language into position over the text.
Swiss Patent 363010 suggests overprinting the familiar and foreign texts using inks of different colors and employing a sheet of the same size as the book incorporating a series of two-color filters which may be positioned over the text so as to reveal either the foreign text or its familiar language translation to the student. This apparatus eliminates the need for the student to shift his gaze when referring to the translation of an unfamiliar word or phrase, but it is difficult to shift this overlay so as to reveal the desired text line and the delay required to manually shift the large sheet incorporating the filters to the required position interrupts the flow of reading the foreign text.